YouTube is really a very different case, and in fact the opposite is the case for text.
For speech, the speaker sets the pace, so the challenge of accessibility is actually twofold: the speaker needs to both be clear and not too fast (or too "efficient").
In text, it's the opposite: the reader sets the pace, so more efficient writing will make reading (at whatever pace) less taxing.
You make a good point and I see where you're coming from. But I've gone through a few text tutorials that just fly through the topics without going into enough depth or examples. I think if you're fairly advanced in a skill, sometimes it's hard to relate to the mindset of someone who is new to it. Like, oh, this is so easy to me, I only need one sentence to explain it. But really it needs a whole paragraph.
It's all a balancing act of course. Like you said, has to be both clear and fast.
For speech, the speaker sets the pace, so the challenge of accessibility is actually twofold: the speaker needs to both be clear and not too fast (or too "efficient").
In text, it's the opposite: the reader sets the pace, so more efficient writing will make reading (at whatever pace) less taxing.